1. Field of the Invention
This invention relates to fluorescent lamps and, in particular, to the attachment of power circuitry to such lamps.
2. Description of Related Art
It is well known in the art to electrically connect fluorescent lamps to primary power sources via a variety of different types of power circuitry. For example, complex ballast circuits are commonly provided to perform a number of power-related functions including, inter alia, the conversion of power from the primary sources to AC voltages and frequencies corresponding to the requirements of respective lamps and the limiting and control of the flow of electrical current to the lamps. In recent years, electronic ballasts have been invented which are substantially smaller than their magnetic ballast precursors while even having the capabilities of performing additional functions, e.g. dimming. If the operating frequency is increased, the size of magnetic and filter components of an electronic ballast can be further decreased. As a consequence of increasing the frequency, however, voltage and current losses tend to increase, particularly because of losses in the impedances of long leads typically used to connect ballasts to lamps. More specifically, the leads have inductive impedances with voltage drops that increase with frequency and parasitic capacitances which bypass current intended for the lamp.
Traditionally, power circuits for fluorescent lamps are incorporated in fixtures for the lamps. This is done primarily because of size, weight, cost and safety factors of such circuits and, especially, in relationship to complex and relatively-heavy ballast circuits. However, if the power circuits can be operationally and cost effectively incorporated in the lamps, rather than in the fixtures, there are many advantages. To name a few:
Each fixture will no longer be limited to use with specific lamp types which are associated with a specific power circuitry installed in the fixture.
It will be impossible for the user to install the wrong lamp in the fixture.
The power circuit and lamp can be optimized to work together to maximize efficiency and lamp life, while minimizing circuit volume and parts count.
Fixtures can be less expensive, more attractive, and have more efficient reflector designs, because they will no longer need to be designed around the power circuitry.
The need for long connection leads will be eliminated, thereby enabling an increase in operating frequency without the consequent increases in voltage and current losses.
High-voltage power circuitry can be contained within the lamp envelope, thereby reducing shock hazards.
While the prior art describes miniaturized power circuitry for fitting within the envelope of a lamp, further development is needed to achieve effective containment of the circuitry within the envelope without adversely affecting operation of the lamp. For example, U.S. Pat. No. 5,485,057 suggests that a circuit module be encapsulated in a heat-transferring material so as to completely fill the end of a lamp envelope. Presumably this is also a gas-impermeable material and it is somehow secured in place and sealed to the envelope to prevent gas leakage either into or out of the lamp. However, no guidance is given as to what material should be used or how it will be secured in place without leakage or separation from the interior lamp envelope wall over the wide range of temperatures that will be experienced in operation. Further development is also needed to facilitate electrical connections to the circuitry. It becomes difficult to make such connections, when the circuitry is contained within the lamp envelope.
It is an object of the invention to provide a fluorescent lamp which is adapted for incorporating circuitry for powering the lamp.
It is another object of the invention to provide such a lamp in which the power circuitry is incorporated without detrimentally affecting operation of the lamp.
In accordance with the invention, a fluorescent lamp comprises a tubular envelope having a sealed light-emissive portion and an integral adjacent portion for containing power circuitry. The light-emissive portion contains longitudinally-separated first and second electrodes and an ionizable gaseous medium. The adjacent portion is physically isolated from the light-emissive portion by a gas-impervious sealed end of the light-emissive portion.
In one preferred form of the invention, the sealed end comprises a stem including leadthrough means, in communication with the sealed light-emissive portion and the integral adjacent portion, for electrically connecting the power circuitry to one of the electrodes.